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ANATOMY2: Structure of the eye > Ciliary body > Flashcards

Ciliary body Flashcards

1
Q

How large is the ciliary body?

A

approximately 5-6mm wide

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2
Q

What is the broad shape of the ciliary body?

A

5-6mm wide ring of tissue that extends from the scleral spur anteriorly to the ora serrata posteriorly

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3
Q

What is the width of the ciliary body temporally vs nasally?

A
  • temporally: 5.6-6.3mm
  • nasally: 4.6-5.2mm
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4
Q

What are the 2 zones into which the ciliary body is divided?

A
  1. Anteriorly: pars plicata (corona ciliaris)
  2. Posteriorly: pars plana

see image: pars plicata = PPL, pars plana = PP

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5
Q

What approximate shape is the ciliary body in cross section?

A

triangular

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6
Q

Where are the base and apex of the triangle formed by the ciliary body in cross section?

A

base: faces anterior chmaber, apex: blends posteriorly with the vascular choroid

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7
Q

How wide is the pars plicata anterior layer of the ciliary body?

A

2mm

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8
Q

What structures form the pars plicata anterior layer of the ciliary body?

A

70 radially arranged folds known as ciliary processes

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9
Q

What are the dimensions of the ciliary processes that form the pars plicata layer of the ciliary body?

A

0.5-0.8 mm in length, 0.5mm wide

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10
Q

Why are the tips of the ciliary processes forming the pars plicata layer of the ciliary body paler?

A

due to decreased epithelial pigmentation

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11
Q

How are different sizes of ciliary processes in the pars plicata arranged?

A

minor ciliary processes may be present in the valleys between the major processes

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12
Q

What is the size of the pars plana?

A

approximately 4mm wide zone

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13
Q

What are the boundaries of the pars plana?

A

extends from the posterior limits of the ciliary processes to the ora serrata, the sharp serrated or dentate junction where non-pigmented ciliary epithelium undergoes a sharp transition to become the neural retina

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14
Q

What is the ora serrata?

A

the sharp serrated or dentate junction where non-pigmented ciliary epithelium undergoes a sharp transition to become the neural retina

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15
Q

What are 3 histological sections that the ciliary body can be divided into?

A
  1. ciliary epithelium
  2. ciliary body stroma
  3. ciliary muscle
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16
Q

What are the 3 principal functions of the ciliary body?

A
  1. accommodation
  2. aqueous humour production
  3. production of lens zonules, vitreal glycosaminoglycans and vitreal collagen
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17
Q

Where within the ciliary body is the ciliary muscle?

A

occupies the anterior two-thirds of the ciliary body

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18
Q

What function does the ciliary muscle work with the lens zonules (suspensory ligament) and the elastic lens fibres and capsule to perform?

A

alter the refractive power of the lens

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19
Q

What are the 3 things which work in conjunction to alter the refractive power of the lens?

A
  1. ciliary muscle of ciliary body
  2. lens zonules (suspensory ligament)
  3. natural elastic nature of the lens fibres and capsule
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20
Q

What is the histological structure of the ciliary muscle portion of the ciliary body?

A

ciliary muscle in meridional sections consists of three groups of smoooth muscle fibre bundles embedded in a vascular connective tissue stroma

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21
Q

What are 3 types of cells present int he vascular connective tissue stroma surrounding the smooth muscle fibre bundles in the ciliary muscle?

A
  1. melanocytes
  2. fibroblasts
  3. occasional immune cells such as mast cells, macrophages and lymphocytes
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22
Q

What are the 3 groups of muscle fibres forming the ciliary muscle of the ciliary body named?

A
  1. outer, longitudinal muscle fibres
  2. middle oblique or radial muscle fibres
  3. inner, circular muscle fibres
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23
Q

What are the anterior attachments of the outer longitudinal muscle fibres of the ciliary muscles?

A

scleral spur and therefore indirectly the corneoscleral trabeculae

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24
Q

What are the posterior attachments of the outer longitudinal muscle fibres of the ciliary muscles?

A

inner aspect of the sclera

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25
Q

What are the inner circular muscle fibres of the ciliary muscle also known as?

A

Müller’s muscles (one of the 3 so-called muscles associated with the eye and adnexa)

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26
Q

Which structure are the middle oblique or radial muscle fibres of the ciliary muscle continuous with?

A

inner corneoscleral trabeculae

27
Q

What is the physical appearance of the inner circular muscle fibres when viewed in meridian sections of the ciliary body?

A

cross-sectional profiles in conventional meridian sections

28
Q

What is the interrelationship between outer longitudinal, middle oblique/radial and inner circular muscles of the ciliary muscle?

A

appears the fibres are all components of an interwoven fibre network (image: as seen on external view with the sclera removed)

29
Q

What is thought to be the action of the ciliary muscle on aqueous outflow?

A
  • contraction of longitudinal, outer ciliary muscle fibres causes inwards and posterior movement of scleral spur
  • also causes effect via extensions of these tendons to the inner wall of canal of Schlemm
  • distends inter- and intratrabecular spaces of TM and prevents collapse of Schlemm’s canal during periods of high pressure

therefore contraction of outer longitudinal muscle fibres increases aqueous outflow according to this evidence

30
Q

Which drugs is the mode of action of the outer longitudinal ciliary muscle fibres on the trabecular meshwork/canal of Schlemm thought to demonstrate?

A

miotic drugs such as pilocarpine (pupil constrictors) - used to increase aqueous outflow facility in patients with glaucoma

31
Q

What is aqueous humour?

A

clear colourless fluid actively secreted by the ciliary processes

32
Q

Which structures actively secrete aqueous humour?

A

ciliary processes of the ciliary body

33
Q

What are the ciliary processes?

A

delicate, finger-like protrusions of loose vascular connective tissue covered by a bilaminar cuboidal/ columnar neuroepithelium, the outer pigmented and inner non-pigmented ciliary epithelium

34
Q

What is the embryological origin of the bilaminar cuboidal/collumnar neuroepithelium of the ciliary processes, that constitutes the major site of the blood-aqueous barrier?

A

both derived embryologically from the double neuroectoderm of the optic cup

35
Q

Which part of the bilaminar cuboidal/columnar neuroepithlium (forming the blood-aqueous barrier) secretes aqueous humour?

A

actively secreted by the inner, non-pigmented ciliary epithelium (on the side of the posterior chamber containing aqueous)

36
Q

Explain the following diagram:

A

at the top is the posterior chamber containing aqueous

top layer of epithelium is the inner, non-pigmented layer

below is the outer, pigmented ciliary epithelium containing melanin granules

below is a fenestrated capillary

37
Q

How are the apices of the aqeous secreting, non-pigmented inner ciliary epithelium connected?

A

junctional complexes including tight junctions

38
Q

What are the cell connections within the outer, pigmented epithelium?

A

held together only by punctate adherentes (macula adherentes)-like junctions or permeable band-like junctions (zonula adherentes)

39
Q

What happens to macromolecules that have passed through the highly permeable fenestrated stromal capillaries and reached the bilaminar ciliary epithelium?

A

the macromolecules pass between pigmented epithelium cells, but then are prevented from passing into the posterior chamber by the non-pigemented ciliary epithelium with junctional complexes connecting the apices

40
Q

What are the morphological features of the inner, non-pigmented ciliary epithelium characteristic of? Give 2 key examples

A

secretory epithelium

  1. numerous mitochondria
  2. histochemically can be shown to contain enzymes necessary for active fluid transport e.g. carbonic anhydrase and ATPase
41
Q

What are the histological features of the non-pigmented, inner ciliary epithelial cells of the pars plana?

A

cuboidal, columnar or irregular, depending on age and location

42
Q

Which part of the ciliary body is thought to play a role in the secretion of zonular fibres, the extracellular vitreal components i.e. collagen and hyaluronic acid, and the inner limiting membrane?

A

the non-pigmented inner ciliary epithelial cells of the pars plana

43
Q

What are 3 things that the non-pigmented ciliary epithelial cells of the pars plana are thought to play a role in secreting (in addition to aqueous humour)?

A
  1. zonular fibres
  2. extracellular vitreal components i.e. collagen nad hyaluronic acid
  3. the inner limiting membrane
44
Q

At what point in life in particular is the non-pigmented inner ciliary epithlium of the pars plana thought to play a role in the production of zonules, vitreal collagen and hyaluronic acid?

A

embyronic development

45
Q

What phenomenon suggests there is traction on the inner non-pigmented epithlium of the pars plana?

A

some of the cells ‘tilt’ anteriorly, suggesting traction by the zonular fibres

46
Q

What merges with the fibrous basal lamina material of the non-pigmented ciliary epithleium of the pars plana?

A

the lens zonules (of Zinn) or suspensory ligament of the lens (alternative name).

47
Q

What is still unclear regarding zonule synthesise?

A

the precise mode of zonule synthesis is unclear

48
Q

Which cells in the pars plana have utlrastrutural and histochemical features that indicate active hyaluronic acid secretion?

A

tall non-pigmented ciliary epithelial cells in the pars plana

49
Q

What are the 2 sites where the blood supply of the ciliary body is derived from?

A
  1. long posterior ciliary arteries - the 2 long posterior ciliary arteries arise from the ophthalmic artery
  2. anterior ciliary arteries
50
Q

What is the course of the long posterior ciliary arteries that supply the ciliary body?

A

arise from the ophthalmic artery

after piercing sclera near the optic nerve head, travel forward in choroid in medial and lateral horizontal plane

divide in the ciliary body before anastomosing with anterior ciliary branches (thus forming major ‘circle’ of the iris)

from this circle arises muscular and recurrent choroidal branches and numerous branches that form the vascular plexus in the ciliary processes

51
Q

What is the course of venous return from the ciliary body? 2 ways

A
  1. occurs predominantly posteriorly through the system of vortex veins
  2. less so through the anterior ciliary veins
52
Q

What are the 3 forms of innervation of the ciliary body?

A
  1. parasympathetic
  2. sympathetic
  3. sensory
53
Q

What is the parasympathetic innervation to the ciliary body? describe the 5 stages of the pathway

A
  1. preganglionic neurone cell bodies are located in Edinger Westphal nucleus
  2. axons travel in the oculomotor (III) nerve
  3. axons synapse with postganglionic cell bodies located in the ciliary ganglion
  4. postganglionic fibres travel to the eye in the short ciliary nerves
  5. terminate as extensive plexus in the ciliary muscle
54
Q

Where does the parasympathetic innervation to the ciliary body terminate?

A

as an extensive plexus in the ciliary muscle

55
Q

Where is the Edinger Westphal nucleus, the origin of parasympathetic innervation to the ciliary body, located?

A

lies posterior to the main oculomotor nucleus in the rostral midbrain at the level of the superior colliculus

56
Q

Which neurotransmitters mediate the action of the parasympathetic nerves supplying the ciliary body, at which receptors?

A

acetylcholine on the muscarinic receptors

57
Q

What is the sympathetic innervation of the ciliary body? 7 key points

A
  1. preganglionic neurone cells bodies situated in the lateral grey horn of the first thoracic segment of the spinal cord
  2. preganglionic fibres relay in the superior cervical ganglion (adjacent to vertebrae C2 and C3 behind the internal carotid artery) with second order neurones
  3. postganglionic fibres leave the ganglion as the internal carotid nerve and plexus
  4. fibres reach the orbit as either: direct branches of the internal carotid plexus OR by joining the ophthalmic division of the trigeminal and its main branch in the orbit, the nasociliary nerve
  5. sympathetic fibres pass directly to the retrobulbar plexus behind the eye or through the ciliary ganglion uninterrupted
  6. from the ciliary ganglion, fibres are distributed via the short ciliary nerves to the blood vessels of the eye, including those in the ciliary body
  7. some terminal filaments of the internal carotid plexus may also be distributed via the ophthalmic artery and its branches
58
Q

What are 3 key steps in the journey of the sympathetic innervation of the ciliary body, BEFORE the nerves reach the orbit?

A
  1. preganglionic neurone cells bodies situated in the lateral grey horn of the first thoracic segment of the spinal cord
  2. preganglionic fibres relay in the superior cervical ganglion (adjacent to vertebrae C2 and C3 behind the internal carotid artery) with second order neurones
  3. postganglionic fibres leave the ganglion as the internal carotid nerve and plexus
59
Q

What are the 2 ways that sympathetic nerve fibres reach the orbit?

A
  1. EITHER: direct branches of the internal carotid plexus
  2. OR: by joining the ophthalmic division of the trigeminal and its main branch in the orbit, the nasociliary nerve
60
Q

Once sympathetic nerve fibres have reached the orbit (via internal carotid plexus or by joining nasociliary nerve) what are 3 aspects of the distribution?

A
  1. sympathetic fibres pass directly to the retrobulbar plexus behind the eye or through the ciliary ganglion uninterrupted
  2. from the ciliary ganglion, fibres are distributed via the short ciliary nerves to the blood vessels of the eye, including those in the ciliary body
  3. some terminal filaments of the internal carotid plexus may also be distributed via the ophthalmic artery and its branches
61
Q

What are the neurotransmitters and receptors involved in mediating the sympathetic action on the ciliary body?

A
  • norepinephrine
  • acts on 2 subclasses of receptors: alpha 1 and beta 2 adrenoceptors
  • both of which are inhibitory
62
Q

Are the 2 subclasses of receptors that norepinephrine acts on to mediate sympathetic innervation to the ciliary body inhibitory or excitatory?

A

both inhibitory

63
Q

What is the sensory innervation to the ciliary body and what is its function?

A

dervied from the nasociliary nerve (branch of ophthalmic division of trigeminal nerve)

function is unknown

64
Q

What structure synthesises and maintains zonule fibres?

A

non-pigmented ciliary epithelium

ANATOMY2: Structure of the eye (14 decks)

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